1. Field of the Invention
The present invention relates to motion detectors, and more particularly, to a planar microwave transceiver and antenna.
2. Description of the Related Art
Area protection sensors and/or intrusion detection systems, such as those used in burglar alarms, typically include presence and/or motion detectors. Two general types of detectors are used: passive and active. An example of a passive detector is a passive infrared detector which detects the presence and/or motion of infrared radiation within a defined area to be protected.
An example of an active detector is a transceiver. The transceiver transmits and receives some form of radiation to detect the presence and/or motion of an object within the defined area to be protected. One example is an acoustic transceiver which transmits and receives acoustic radiation (e.g., ultrasonic, SONAR) to perform its detection function. Another example is a microwave transceiver transmits and receives microwave radiation (typically frequencies greater than 1 Gigahertz) to perform its detection function.
A microwave transceiver typically generates microwave radiation by way of a waveguide cavity oscillator. The microwave radiation is radiated into free space by way of a waveguide horn antenna (See FIG. 1). The transceiver and horn antenna are often contained in a plastic housing which is mounted on the wall of a dwelling or building to be protected. While the waveguide cavity oscillator and horn antenna effectively generate, radiate, and collect microwave radiation, they suffer from the disadvantage of being physically large and heavy. Thus, the plastic housings which contain the transceivers and horn antennas are rather bulky in order to accommodate the considerable physical dimensions of the components. When mounted on the wall of a home or place of business, these bulky plastic housings are quite noticeable and detract from the aesthetics of the area to be protected. It has become clear in the intrusion detection device market that consumers prefer a smaller and more compact unit which is less conspicuous.
The waveguide cavity oscillator and horn antenna also suffer from the disadvantage of being expensive to produce. Waveguide oscillators generally use Gunn diodes as the active oscillator device. Gunn diodes are specialized devices which makes them expensive. Horn antennas and waveguide oscillator cavities are expensive because they are usually manufactured by a casting process. Naturally, consumers prefer a unit which has a low cost.
Hence, a compelling need has emerged for a more compact and inexpensive microwave transceiver and antenna for use in intrusion detection systems.